1. Field of the Invention
The present invention relates to an expansion valve, and in particular, to an expansion valve that is provided in a refrigeration cycle to control the flow rate of a refrigerant to be delivered to an evaporator.
2. Description of the Related Art
The refrigeration cycle of an automotive air-conditioner generally comprises: a compressor for compressing a circulating refrigerant; a condenser for condensing the compressed refrigerant; a receiver for separating the condensed refrigerant into vapor and liquid; an expansion valve for throttling and expanding the separated liquid refrigerant to change it in a mist state and for delivering the misty refrigerant; and an evaporator for evaporating the misty refrigerant to cool the air in a vehicle interior by the latent heat of vaporization.
As the expansion valve, a thermostatic expansion valve is used, which opens and closes, by sensing a temperature and a pressure of the refrigerant on the outlet side of the evaporator, a valve portion such that the refrigerant delivered from the evaporator has a predetermined degree of superheat in order to control the flow rate of the refrigerant to be delivered to the evaporator. In the body of the expansion valve, a first passage for making the refrigerant moving from the receiver to the evaporator pass through and a second passage for making the refrigerant, which has returned from the evaporator, pass through to deliver it to the compressor are formed. A valve hole is formed in the intermediate portion of the first passage, and a valve element for adjusting, by attaching and detaching the valve hole, the flow rate of the refrigerant moving to the evaporator is arranged. A power element for controlling, by sensing the temperature and pressure of the refrigerant flowing through the second passage, an opening degree of the valve portion is provided at the end portion of the body. The drive force of the power element is transmitted to the valve element via a lengthy shaft. The shaft extends so as to cross the second passage and reach the first passage, and is slidably supported by an insertion hole provided in a partition wall by which the first passage and the second passage are partitioned from each other in the body.
Such an expansion valve is installed in an engine room of a vehicle, a vehicle interior, or a partition wall by which the former two are partitioned from each other, and a plurality of pipes are connected thereto via plate-shaped joints (see, e.g., Patent Document 1). That is, the pipe extending from the receiver is connected to the inlet port of the first passage in the body of the expansion valve, and the pipe extending toward the evaporator is connected to the outlet port. Further, the pipe extending from the evaporator is connected to the inlet port of the second passage, and the pipe extending toward the compressor is connected to the outlet port. Each of the pipes is fixed to the expansion valve by, for example, inserting a lengthy bolt through a mounting hole that is formed to penetrate the body of the expansion valve and by tightening the aforementioned joint to the body.
Because an aluminum material, etc., which is excellent in weight saving or processability, is often used in the bodies of such expansion valves, the coefficient of thermal conductivity of the body is relatively high. Accordingly, it is concerned that the temperature of the high-temperature refrigerant on the upstream side from the valve hole in the first passage, or the temperature of the low-temperature refrigerant on the downstream side from the valve hole therein, may be transmitted to the power element via the body, thereby causing a bad influence on the operation of the expansion valve. That is, there is the possibility that a temperature sensing error may be caused in the power element due to the transmission of the temperature on the first passage side. Thus, a technique is proposed, in which the heat transfer from a first passage to a power element is suppressed by, for example, separately forming, with machining, a space between the first passage side and a second passage (see, e.g., Patent Document 2).